The present invention relates generally to hydraulic apparatus and, more particularly, to flexible hoses for communicating hydraulic fluid between a deployable ram air turbine powered hydraulic pump, and the hydraulic system of an aircraft.
The hydraulic return fluid, also known as the pressure fluid, for an aircraft is furnished by a hydraulic pump powered by a propulsive engine or by a turbine having rotatable blades located in and turned by the airstream adjacent the fuselage when the aircraft is airborne. As an aircraft typically has redundant backup systems, it may use both of the foregoing power sources to power, respectively, several hydraulic pumps. The latter power source is commonly referred to as a ram air turbine. A hydraulic pump is commonly attached to the ram air turbine, and directly powered by the turbine's drive shaft. The ram air turbine and attached pump together form a hydraulic power assembly.
Such a hydraulic power assembly is used in two ways. Firstly, it is rigidly mounted external to the fuselage so that the ram air turbine is always exposed to the airstream and thus operates whenever the aircraft is airborne. Alternatively, the assembly is stored in an up position out of the airstream of the airborne aircraft or is housed within the fuselage and rotatably deployed into the airstream of an airborne aircraft only when called on in an emergency.
The rigidly mounted, permanently deployed hydraulic power assembly is commonly called an auxiliary power unit, and is used to generate continual hydraulic return fluid whenever the aircraft is airborne. The deployable hydraulic power assembly is rotated into the airstream only in an emergency, for example, the failure of an engine or a hydraulic pump powered by a main engine, or running out of fuel.
Storing the hydraulic power assembly in an up position or housing it within the fuselage and deploying it only when necessary offers several advantages over using a permanently deployed auxiliary power unit as an emergency backup for hydraulic return fluid. Firstly, the deployable configuration reduces the coefficient of drag for the aircraft because the ram air turbine is seldom going to be exposed to the airstream. Secondly, since the rotatable blade and connected turbine will be rotating only during an emergency, the aforementioned components need not be engineered to the same demanding specifications as an auxiliary power unit generating the same hydraulic return fluid. This results in a savings in cost and weight, as well as an improvement in reliability.
The hydraulic power assembly is typically attached to one end of a strut, with the other end of the strut being mounted on a trunion attached to the airframe. The hydraulic power assembly is deployed by activating an actuator which rotates it around the trunion. The challenge posed by the foregoing configuration lies in communicating the hydraulic fluid between the hydraulic pump of the hydraulic power assembly and the hydraulic system of the aircraft, given the necessary rotation of the hydraulic power assembly relative to the airframe. A conventional approach to this problem is shown in FIGS. 1, 2 and 3.
More particularly, FIG. 1 is a side view of ram air turbine 21 in its deployed position. Ram air turbine includes blades 23. Hydraulic pump 25 is attached to and powered by ram air turbine 21. Hydraulic power assembly 26 is comprised of ram air turbine 21 and hydraulic pump 25.
Strut 27 includes distal end 29 and proximal end 31. Hydraulic power assembly 26 is attached to distal end 29. The foregoing are integral components of aircraft 33, which also includes airframe 35, fuselage skin 37 and trunion 39. The position of hydraulic power assembly 26 in its stowed position within fuselage skin 37 is shown in phantom.
FIG. 2 is a front view of proximal end 31 of strut 27 and illustrates its connection to airframe 35 in greater detail. Proximal end 31 is attached to hydraulic swivel 41 and is also mounted on trunion 39 by means of coaxial annular openings 42 and 43, allowing strut 27 and hydraulic power assembly 26 to rotate about axis of rotation 44.
Referring again to FIG. 1, hydraulic power assembly 26 is deployed by means of actuator 45. Actuator 45 is fixedly attached to airframe 35 and rotatably attached to proximal end 31 of strut 27 at pivot 47. Return tube 49 and supply tube 51 fluidly communicate hydraulic fluid between hydraulic swivel 41 and hydraulic interface 53. Tubes 49 and 51 are rigid metal tubes. The hydraulic system for aircraft 33 fluidly communicates with hydraulic interface 53.
FIG. 3 is a frontal section view of hydraulic swivel 41. Hydraulic swivel 41 includes fitting 55, journal housing 57, and annular seals 59. Fitting 55 is located over and around journal housing 57, and in slidable abutment thereto. Journal housing 57 includes attachment flange 61. Proximal end 31 of strut 27 is attached to hydraulic swivel 41 and journal housing 57 at attachment flange 61. Thus, hydraulic power assembly 26, strut 27 and journal housing 57 are free to rotate about axis of rotation 44, relative to fitting 55 and airframe 35.
Journal housing 57 contains return passageway 63 and supply passageway 65. Fitting 55 contains return passageway 66 and supply passageway 67. Return conduit 68 in strut 27 fluidly communicates with pump 25. Return passageway 63 fluidly communicates return passageway 66 with conduit 68. Return passageway 66 is sealably connected with return tube 49. Thus, the return hydraulic fluid from pump 25 fluidly communicates with hydraulic interface 53.
Supply conduit 69 in strut 27 fluidly communicates with pump 25. Supply passageway 65 fluidly communicates supply passageway 67 with supply conduit 69. Supply passageway 67 is sealably connected to supply tube 51. Thus, the supply hydraulic fluid from hydraulic interface 53 fluidly communicates with pump 25.
As may be discerned from the foregoing description, seals 59 are necessarily composed of a flexible material, yet are subjected to pressure, corrosive hydraulic fluid, and friction from the rotation of journal housing 57 relative fitting 55. Thus, as is typical for devices having fluid seals, the reliability and life of hydraulic swivel 41 is primarily limited by the reliability and life of seals 59.
Furthermore, should seals 59 stick or otherwise fail to allow the free rotation of journal housing 57 relative to fitting 55, fitting 55 would be subjected to torque about axis of rotation 44. Since fitting 55 is coupled to return tube 49 and supply tube 51, the application of such torque would create a lateral force against fitting 55 and, more particularly, against the respective connections between return tube 49 and return passageway 66, and supply tube 51 and supply passageway 67. As neither fitting 55 nor the respective connections are designed to resist lateral force, such loading could cause the leakage of hydraulic fluid from hydraulic swivel 41.
In addition to concerns over leakage, the sticking of seals 59 could cause crimping in tubes 49 and 51, which would restrict the flow of hydraulic fluid therethrough. With respect to supply tube 51, crimping could result in the supply flow dropping low enough to cause cavitation in the supply flow to pump 25, resulting in vaporization of hydraulic fluid and, ultimately, the failure of pump 25 to maintain the return pressure above the required minimum operational level.
Given the requirements that hydraulic swivel 41 communicate hydraulic fluid without leaking and that journal housing 57 rotate relative to fitting 55, the components of hydraulic swivel 41 must be machined to very narrow tolerances. The manufacture of hydraulic swivel 41 is thus expensive. Furthermore, great care must be taken to colinearly align the axis of rotation of journal housing 57 relative to fitting 55, with axis of rotation 44 because misalignment would result in part of the considerable weight of hydraulic power assembly 26 and strut 27 being resisted by hydraulic swivel 41. The entirety of the foregoing weights is intended to be resisted solely by trunion 39. As hydraulic swivel 41 is not designed to resist such force, misalignment could result in movement, bending or fracture of one or more of its components, and ultimately occasion leakage.
U.S. Pat. No. 5,484,120 issued to Blakeley et al. also shows a deployable ram air turbine. More particularly, in column 3 at lines 11-15 and column 8 at lines 19-22, Blakeley et al. disclose using hydraulic lines to transfer power generated by a deployed ram air turbine through the strut to the aircraft.
Based on the foregoing, it can be appreciated that there is a need in the art for fluidly communicating hydraulic fluid between the pump on an articulated ram air turbine and the hydraulic interface of an aircraft, in a manner which overcomes the above-described disadvantages, shortcomings and limitations of the prior art. The present invention fulfills this need in the art.